The potentiodynamic polarization curves of coatings and substrate(Q235) in 3.5% NaCI solution are shown in Fig.1. The corrosion potential(Ecorr) and corrosion current density(Icorr) of coatings are shown in Table 1, which are calculated by potentiodynamic polarization curves. The corrosion potential Ecorr of Zn-Al coating is -1.243±0.005 V, the corrosion potential of Zn-Al-Mg-TiO2 coatingis-1.276±0.002 V, and the corrosion potential of substrate(Q235) is -0.647±0.004 V. The corrosion potentials of Zn-Al coating and Zn-Al-Mg-TiO2 coating are in the negative direction of the corrosion potential of substrate (Q235). The reason for this phenomenon is that the corrosion potential of active metals such as Zn and Al, etc. in the coating are more negative relatively. The coating with more ne-gative corrosion potential can provide sacrificial anodic protection for the substrate (Q235).
In addition, the corrosion current density of Zn-Al-Mg-TiO2 coating is 15.56 uA/cm2, which is much lower than the corrosion current density of the Zn-Al coating, indicating that thecorrosion resistance of Zn-Al-Mg-TiO2 coating is better than Zn-Al coating in 3.5% NaCI solution.
Table 1
The electrochemical parameters of potentiodynamic polarization curves.
Fig. 1. The potentiodynamic polarization curves of Q235, ZneAl coating and Zn-Al-Mg-TiO2 coating
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